1. Field of the Invention
This invention relates to package or cartridge mechanical seals for providing a fluid tight seal between a rotatable shaft and a housing. This invention relates especially but not exclusively to such seals for use with pumps, especially centrifugal pumps, in which the cartridge seal is located within the housing and extends along the shaft. Although reference is made herein to centrifugal pumps, it should be understood that mechanical seals of the invention have use in other mechanical seal applications.
2. Brief Description of the Related Art
A conventional mechanical seal comprises a "floating" component which is mounted axially movably around the rotary shaft of, for example, a pump and a "static" component which is axially fixed, typically by being secured to a housing. The floating component has a flat annular end face, i.e. its seal face, directed towards a complementary seal face of the static component. The floating component is urged towards the static component to close the seal faces together to form a sliding face seal, usually by means of one or more springs. In use, one of the floating and static components rotated; this component is therefore referred to as the rotary component. The other of the floating and static components does not rotate and is referred to as the stationary component.
The rotary and stationary components may also be referred to as the rotational and non-rotational components (or portions) of a seal, respectively.
Those seals whose floating component is rotary are described as rotary seals. If the floating component is stationary the seal is referred to as a stationary seal.
The radially inner side of a sliding face seal may in use be supplied with a barrier fluid, which serves to protect against possibly noxious liquid which may leak through the seal from contacting pump parts in undiluted form as well as to cool and lubricate the seal. A second seal is required to keep the barrier fluid to its proper place on the radially inner side of the sliding face seal. The entire seal device is therefore a double mechanical seal or, more simply, a double seal.
Mechanical seals may be assembled in situ from separate pieces or sub-assemblies. However, it is more convenient for the user for a seal to be assembled in the factory into a self-contained unit, customarily referred to as a cartridge.
A representative prior art seal for a centrifugal pump is that sold by Durametallic Corp. under the designation "Double-HS/RA-Seal". This is a double seal for mounting around a pump shaft extending through a bore in the housing of a centrifugal pump. The seal components are held together in the form of a cartridge, except for a rotary static sliding face seal component to be installed in the back of the pump impeller and for two O-rings associated with said component. The cartridge comprises a sleeve which can be fitted over the pump shaft and around which the other cartridge components are arranged, and which is installed by being pressed by hand into the bore in the housing. The cartridge then comes to rest against a shoulder provided on the pump housing. The location of the cartridge must be measured and compared with the manufacturer's instructions. The rotary static component separate from the cartridge is installed in the back of the impeller, which is then secured to the shaft, in this case by mating of an internal screw thread of the impeller with an external screw thread at the free end of the shaft. Such seals, therefore, are not convenient to install and great care is required to ensure that the seal is installed to match the longitudinal clearance of the pump.